Silicas powders

Fig. 230 Adsorption of nitrogen at 77 K on a silica powder a) adsorption isotherms b) /-plot. Broken line, uncompacted powder continuous line, power compacted at 2-00 x 10 N m (130 ton in ). (—>—) adsorption (—<-) desorption. / is the ratio of the amount adsorbed on the powder to the amount adsorbed on the compact at the same relative...

Examples are provided by the work of Carman and Raal with CF2CI2 on silica powder, of Zwietering" with nitrogen on silica spherules and of Kiselev" with hexane on carbon black and more recently of Gregg and Langford with nitrogen on alumina spherules compacted at a series of pressures. In all cases, a well defined Type II isotherm obtained with the loose powder became an equally well defined Type IV isotherm with the compact moreover both branches of the hysteresis loop were situated (drove the isotherm for the uncompacted powder, but the pre-hysteresis region was scarcely affected (cf. Fig. 3.4). The results of all these and similar... 

Fig. 3.20 Pore size distributions (calculated by the Roberts method) for silica powder compacted at (A) Ibtonin" (B) 64tonin (C) 130 ton in". The distributions in (a) were calculated from the desorption brunch of the isotherms of nitrogen, and in (h) from the adsorption branch.

The evidence obtained in compaction experiments is of particular interest in the present context. Figure 3.22 shows the results obtained by Avery and Ramsay for the isotherms of nitrogen on compacts of silica powder. The hysteresis loop moved progressively to the left as the compacting pressure increased, but the lower closure point did not fall below a relative pressure of 0-40. Similar results were obtained in the compaction of zirconia powder both by Avery and Ramsay (cf. Fig. 4.5), and by Gregg and Langford, where the lower closure point moved down to 0-42-0-45p° but not below. With a mesoporous magnesia (prepared by thermal decomposition of the hydrated carbonate) the position of the closure point... 

Fig. 3.22 Adsorption isotherms of nitrogen at 77 K on silica powder and its compacts. (A) uncompressed (B) 10 ton in (C) 40 ton in" (D) 50 ton in (E) 100 ton in . Open symbols represent adsorption, solid symbols desorption. (Courtesy Ramsay.)...

Fig. 3.26 Comparison plots for compacts of silica and magnesia. In each case the adsorption of nitrogen at 78 K on the compact is plotted against that on the uncompacted powder, (a) and (b), comparison plot and adsorption isotherm for silica powder compacted at 130 ton in (c) and (d), comparison plot and adsorption isotherm for precipitated magnesia compacted at 10 ton in. Note that the upward sweep of the comparison plot commences at a relative pressure below the inception of the loop.

Transparent fused silica can be formed at a temperature of 1200°C and a pressure of 13.8 MPa (2000 psi) from silica powder consisting of 15 nm ultimate particles (92) or by electric arc fusion of pure silica sand having low iron and alkali metal contents. The cooled product is ground to the desired particle size. Fused sihca is primarily manufactured by C-E Minerals, Minco, and Precision Electro Minerals in the United States by Chuo Denko, Denki Kagaku Kogyo, NKK, Showa Denko, and Toshiba Ceramics in Japan. Based on 1988 data and projected growth, an estimated 135,000 metric tons of fused siUca were used in 1994 as a sacrificial component or investment casting in the manufacture of metals and as a component in refractory materials (62). 

Effect of pH on the rate of silica extraction from vitreous silica powder at 80°C (after El-Shamy and Douglas, 1967)... 

Microporous insulation materials consist mainly of highly dispersed silica with a particle size of only 5-30 nm. The highly dispersed silica powder is pressed to plates, which receive heat treatment up to 800 °C, after which the plates are self-supporting and possess a micropore structure with pore diameter of 0.1pm. The addition of opacifiers to the highly dispersed silica starting material reduces the loss of heat by radiation. The dates for such insulation boards are shown in Table 18. 

Sieve all the feldspar potash, ball clay, kaolin and silica powder by mesh, size 90 pm. 

Table 17.2 presents results of physical-chemical testing of the silica powders. The A1 sample has the lowest Cetultrimethyammonium bromid (CTAB) and Brunaues, Emmett, and Teller (BET) surface area, higher structure (DBF) and more silanol (-OH) groups on surface per unit area. 

In our previous paper [6], the authors have demonstrated that production of fine silica powder is possible by phase hydrolpis of tetramethoxysilane fTEMS). In this communication, we report the effect of the shape of reactor and operational condition, especially mixing condition on conversion of the reaction and properties especially diameter of produced silica fines. 

The auto-thermal reaction of ethanol occurred in the shell side of a palladium membrane reactor in which a Zn-Cu/AlaOs industrial catalyst (MDC-3) was packed with silica powder. Ethanol-water mixture (nH2o/nEioH=l or 3) and oxygen (noa/nEioH=0.2,0.776 or 1.035) are fed concurrently to the shell side. The reaction temperatures were set at 593-723 K and the pijrasures were 3 10 atm. 

Liquid hydrocarbons have been adsorbed on silica powder and dispersed in the agar medium. The silica may be autoclaved (Baruah et al. 1967), though this may be avoided by sterilizing the silica by heating, and carrying out the sorption and removal of solvents such as acetone or dichloromethane under sterile conditions. 

Silica powder has been studied as a stabilizer for oil well cement at high temperatures [1895]. Tests indicated that silica powder can improve the stability and pressure resistance strength of cement. The manufacture of very-high-strength concrete (after 28 days the compressive strength is greater than... 

The structure of the metal particles dispersed on a silica powder support ( Aerosil 380, 70 A average silica particle diameter) has been studied by Avery and Sanders (47) using electron microscopy in both bright and dark field, to determine the extent to which the metal particles were multiply twinned or of ideal structure. Platinum, palladium, and gold were examined. These catalysts were prepared by impregnation using an aqueous solution of metal halide derivatives, were dried at 100°-150°C, and were hydrogen... 

Kanan, S.M., Tze, W.T.Y., and Tripp, C.P. (2002) Method to double the surface concentration and control the orientation of adsorbed (3-aminopropyl)dimethylethoxysilane on silica powders and glass slides. Langmuir 18(17), 6623-6627. 

Chiu, C. Y. Chiang, A. S. T. Chao, K. J. 2006. Mesoporous silica powders and films—Pore size characterization by krypton adsorption. Microporous Mesoporous Mater. 91 244-253. 

Instead of blending them either by dispersing silica powders as fillers within PE, which is a well-developed technology with many applications, or by polymerizing ethylene within the pores of modified9 or unmodified silica,10 now the nanometric physical blending... 

Silica powder, Unstated salt Anon., Loss Prev. Bull., 1987, (078), 9... 

Au and AuPt nanoparticles were assembled on carbon black (XR-72C) or silica powders with a controlled weight ratio of the metals (Au or AuPt) vs. the support materials. The actual loading was determined by thermogravimetric analysis (TGA) and DCP-AES analysis. 

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